Potential issue and solutions: standing water

[KarenRei]

On my way to work today, we swerved at the last minute to avoid a huge, deep pool of standing water on the road, and I got to thinking, what if I had been in an Aptera and we'd gone into it? The prospect of batteries shorting through the water with water entering the passenger compartment is a definitely Not Good(TM) situation. Sure, lead-acid batteries short in cars when they flood, but there's a *lot* less current flowing than we'd have here. Here are some potential ways to ameliorate the problem.

1) Drive wheel

The first part of the vehicle to have the potential for a short, just from my mental image of the layout of the internals of the vehicle, would be the rear drive motor. It's not in-wheel, which buys you some height, perhaps a foot, foot and a half. There's a rather simple solution for this one: a circuit breaker or fuse closer to the batteries.

2) Batteries and ultracapacitors

This one seems a bit trickier. You can't just put a fuse on the batteries because the short is between the terminal. But there still are a few potential solutions. I'll refer to batteries and ultracapacitors interchangeably here.

2a) Internal fuses: The batteries could be waterproof-sealed with internal fuse. This, however, would be a design issue up to the battery manufacturer.

2b) Sealed battery compartment with internal fuse: This would be something Aptera could do on their own -- to have the entire battery pack enclosed in vaccuum-sealed plastic with a fuse between the exterior terminals and the batteries.

2c) Fuses/breakers between batteries in parallel: To get more voltage, many batteries are undoubtedly wired in parallel in places. Breaking the circuit here wouldn't stop them from shorting, but would lower the voltage in the water, making it more likely to take a "direct" route across the terminals and thus having less current travelling through the water at greater distances.

3) Passenger compartment:

3a) Insulative firewall without holes: There's usually a firewall between the batteries and the passenger compartment. If it had a high dielectric constant, that'd make it a longer route for the current shorting through the water to reach the inside of the passenger compartment. How rapidly current drops off in water should be relative to the voltage and the distance, so anything that decreases the voltage or, in this case, increases the distance, is a good thing.

3b) Watertight or water-resistant doors: Having the vehicle be able to float would, on its own, be a good thing.

I think the ideal situation would be internal fuses on the batteries and fuses/breakers for all other electric components that have the potential to carry significant current, such as the drive wheels. Given this, I don't think there'd be a real problem with being shorted in the water, although I'd be more comfortable if tests were done.

[LQUAN]

Internal fuse that built inside the sealed battery pack would be the way to go. I think Toyota is already doing this for their Prius. One fuse to take care of the issue is more cost effective than multiple fuses inside the battery pack.

This car ain't gonna float when you drive it into deep water. Notice the exhaust vents at the rear next to the license plate. I am sure there are other intake vents at the front where the wippers locate. There has to be water sensors in several places to detect water and blow the fuse before it get shorted at the appliance level - e.g. motor and cabin electronics.

If this car chassy is made out of fiberglass, then we have insulation. However, if carbon fiber is used, you will be electrocuted if the car is submerged in water. Carbon fiber is conductive. I'd already tested it myself. Very low resistance if I may add.

[KarenRei]

Who has said fiberglass? I've always heard carbon fiber. There's a big difference.

There are two kinds of carbon fiber -- graphitic and turbostatic. They have different dielectric constants. Also, the ratio of CF to plastic binder in the composite and what type of plastic matters as well.

Good point about the exhaust vents -- they use them to fill in the wake turbulence. Of course, one could always make use of a one-way valve there (they're simple and cheap, just a lightly spring-loaded piece of metal that water pressure would push shut) The only reason I even considered the possibility of it floating was that it's a rather light vehicle with doors designed to be tight-fitting to reduce drag, AFAIK, so it sounded like a possibility.

[Aptera#965]

Now how cool would that be?

An amphibious Aptera :p

Tell me it wouldn't make for a great submarine :D

[KarenRei]

Lol. Not sure I'd want to take it *that* far ;) On the other hand, could you picture the following situation: you and a friend don alien costumes, drive Aptera into body of water, then surface in crowded location. The car's scarab doors open and you match out of the vehicle, scanning the crowds. Perhaps holding fake rayguns.

I plan to have fun with mine. Perhaps not that extreme, but I want to play up the fact that the car looks like you just landed from Mars. ;) You know, perhaps driving around wearing shiny tight-fitting clothing like a B-movie sci-fi space suit, put my hair up weird, etc.

[Prestadude]

"I plan to have fun with mine. Perhaps not that extreme, but I want to play up the fact that the car looks like you just landed from Mars. You know, perhaps driving around wearing shiny tight-fitting clothing like a B-movie sci-fi space suit, put my hair up weird, etc."

What do you mean play up? That's my current driving attire!

[3-4-me]

Ever since it started raining around here, I've been wondering if Aptera was out running the car up and down the road testing it.
You would have to believe they've thought far enough ahead to account for a dose of water.
Aptera is trying to make this vehicle as safe as possible. Voltage containment has to be at the top of the list.:eek:

[LQUAN]

KarenRei,

I always thought this composite car is mainly fiberglass with graphitic carbon fiber strands reinforced. Like most light composite structure I am familiar with (e.g. sailplanes), the structure is mainly weaved fiberglass cloth with sandwiched carbon fiber strands layout in lattice arrangement. The whole thing would be bonded using epoxy resin inside high pressure positive and negative mold. Heavy composite structure such as small leisure boats are mainly stranded fiberglass and epoxy resin. But I could be wrong of method Aptera uses.

[qpham63]

Internal fuse that built inside the sealed battery pack would be the way to go. I think Toyota is already doing this for their Prius. One fuse to take care of the issue is more cost effective than multiple fuses inside the battery pack.

This car ain't gonna float when you drive it into deep water. Notice the exhaust vents at the rear next to the license plate. I am sure there are other intake vents at the front where the wippers locate. There has to be water sensors in several places to detect water and blow the fuse before it get shorted at the appliance level - e.g. motor and cabin electronics.

If this car chassy is made out of fiberglass, then we have insulation. However, if carbon fiber is used, you will be electrocuted if the car is submerged in water. Carbon fiber is conductive. I'd already tested it myself. Very low resistance if I may add.


I am sure this has been though through and addressed. You must build cars that will be run in foul weather to be weather tight as well as any possible splashed or submerged component must be able to with stand the hydraulic pressure of submersion.

Submarines are electric powered...They are okay in conductive salt water. You have to know that you will have a problem and have to design for it.

Regarding the carbon fiber. True, your more expensive spark plug wires are carbon filament. Remember though for the graphite to work, it must be support by resin most likely epoxy or may be phenolic to support the graphite fibers so that it can carry the load.

Although conductive, in a resin matrix like this, it is like copper wires encased in plastic as in your electrical wires. In fact, when space structure and aircraft structures are built and bonded from sub components, great care is taken to assure a ground path such as simple sanding to expose the graphite fibers and installing grounding straps to staking with silver filled epoxy to the tune of $300/oz. or to dope the resin with conductive materials such as milled graphite similar to the way silver is doped into the staking adhesive.

I would never use carbon fiber any where near wiring or as part of the battery enclosure. Remember that if the components are graphite, you would just have to ad a layer of kevlar or glass to the outside to prevent a conduction path. The resin would work but can be scratched through.